You might have seen this YouTube montage of drunk animals. If you haven’t, it’s one for a rainy day. Apart from being amusing, this video raises some questions (at least according to the youtube video comments), such as how do animals get drunk in the wild?

Lots of food that animals eat in the wild (fruit for example) ferments naturally, producing ethanol that can be up to 5% in alcohol content (perhaps not much for a human but a lot more to a tiny mammal).

Some animals are careful to avoid drinking alcoholic fruit juice, as unsurprisingly, being drunk can have negative side-effects.

However, lots of mammals such as pentailed treeshrews, slow lorises, plantain squirrels and several varieties of rats all feed on nectar from the Malaysian bertam palm tree, which can be up to 3.8% in alcohol content. These small mammals act as pollinators, in return gaining a tasty nectar treat. However, despite there being a relatively high alcohol content in this drink of choice for these small fluffy creatures, they don’t seem to be acting too drunk.

Similar effects have been found in other animals. For example, Syrian hamsters (Mesocricetus auratus) drink what is described by scientists as ‘a very high ethanol intake’, yet they seem to be very good at holding their drink.

A recent study by Lupfer and colleagues from the University of Alaska in Anchorage investigated ethanol consumption in another hamster, the dwarf hamster Phodopus campbelli. The researchers gave hamsters set amounts of ethanol to see how much they would have to drink before having any impairment to their motor skills. To measure this they used what is called the ‘Wobbling Scale’ which is exactly what you might expect it to be:

The ‘Wobbling Scale’, copied from Lupfer et al. 2015

The researchers gave the hamsters the ethanol in two ways: either orally or injected directly into their body (i.e. an ‘intraperitoneal’ injection). As expected, the more ethanol that was injected into the hamster’s bodies, the more they ‘wobbled’ according to the scale. However, the hamsters could manage much higher doses of ethanol taken orally without any impairment to their motor control. In fact, they could drink around 10 times the amount of ethanol a human could handle before behaving drunk.

Hamsters could drink an awful lot and still not act drunk. Photo Credit: Bob Travis

So how do the hamsters do this? It seems likely that an enzyme, alcohol dehydrogenase, that we also have as our primary defence against alcohol, is particularly active in these hamsters. However, other studies have also found that another hamster (the Syrian hamster) is not only highly tolerant to ethanol, but also to amphetamines. This might imply that there could be another mechanism in hamsters (such as dopaminergic neurons or something else in the central nervous system) keeping these fellas sober.

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